Migration of river herring

When cormorants appear on the rocks below the Brunswick-Topsham hydroelectric dam and falls of the Androscoggin River, I know the annual run of river herring has begun. There are probably other signs — such as the water temperature — but I rely on the cormorants to tell me what is happening below the river’s surface. From what is seen, I become aware of what is unseen: the blueback herring and alewives that begin their great migration from the ocean, swimming upstream along our major rivers, the St. Croix, Penobscot, St. George, Damariscotta, Sheepscot, Kennebec and Androscoggin, as well as any number of lesser tributaries. Upriver they swim, determinedly against the river’s flow that is swollen by the spring runoff; determinedly too because they are hunted, the prey of any number of predators, including osprey and eagles, larger fish, and, of course, cormorants. The migration begins in early May and typically lasts well into June.

like Jesus hanging from the crosscormorants dry their wingsbeneath the river’s dam

On the Androscoggin, and several other of the major rivers as well, the passage of the river herring to their spawning grounds upriver is blocked by concrete dams. At the Brunswick-Topsham dam they have a man-made fish-ladder to assist them. It’s a long concrete fishway, with a series of locks that the alewives will follow until they get to the pool at the top, where they will be sucked up into a holding tank on a truck, which will deliver them to their spawning grounds at various upriver locales. To get to that fishway, the alewives, blueback herring and occasional salmon must pass through a gauntlet of waiting cormorants. With their bodies half-submerged in the river, the cormorants patrol the river … with only their long necks and heads sticking up out of the water, looking very much a submarine’s periscope.

If you were to judge the contest between cormorant and an alewife based on how cormorants look when they are trying to gain altitude as they take off from the water, you might be inclined, as I have been, to give the fish better than even odds of escape. Cormorants flap wildly, their webbed feet seemingly a drag impeding their ascent, until somehow, eventually, they begin to rise, tuck their legs against their torso and fly away. It’s hardly elegant.

I hadn’t given much thought to how they perform underwater … until I came upon a YouTube video taken with an underwater camera showing a cormorant in hot pursuit of a fish. Like penguins and puffins and other birds that hunt their prey underwater, cormorants are really designed more for their underwater activities than those above. The cormorant zigged and zagged, following its prey like a heat-seeking missile. I would not want to be an alewife with a cormorant on my tail. More often than not, I’m guessing, the cormorant gets its prey. How it’s able to swallow that fish whole remains a mystery to me, for I cannot imagine that a speared alewife or blueback herring surrenders its one life passively, without a struggle. Eventually, either because its gullet is full or it needs a breath of air, a cormorant surfaces, then lets the current take it downstream until quick as a wink, it disappears below the surface to renew the hunt.

how strong the pullswimming against the flowalewives keep on going

A “Maine River Herring Fact Sheet” posted on the Department of Marine Resources website provides some answers to the question “Why are alewives important to the state of Maine?”

What’s interesting to me is that all the reasons listed regard alewives as serving some higher purpose than their own right to swim freely, feed, spawn and swim back to the great ocean again. Namely, their purpose is to be eaten by other creatures. And so, we learn “they provide an alternative prey item for osprey, eagles, great blue heron, loons and other fish-eating birds at the same time juvenile Atlantic salmon are migrating downriver.” Not only that. They also “provide cover for upstream migrating adult salmon that may be preyed on by eagles or osprey, and for young salmon in the estuaries and open ocean that might be captured by seals.”

How lucky salmon are to have so many alewives providing “cover,” giving themselves up that Salmo salar might live!

It doesn’t end there. Alewives provide “revenue” for 35 towns that sell “commercial harvesting rights to alewives on 39 streams and rivers.” These alewives are “recognized” for “the value” they provided as “preferred bait for the spring lobster fishery.”

Lucky for alewives, then, that each female produces 60,000 to 100,000 eggs. Those eggs hatch in about three days, at which point, it seems, alewives are fair game for just about every other species with which they share their freshwater spawning habitat. From mid-July to early November, the young alewives begin their seaward migration. How many actually make it depends upon “the availability of feed in the lakes, the total numbers of young produced in a particular watershed, and the length of time they remain in the freshwater environment.”

as above, so belowso many alewives self-sacrificesalmon are more worthy